Drastic solid-state fluorescence enhancement behaviour of imidazo[4,5-a]naphthalene-type fluorescent hosts upon inclusion of polyethers and tert-butyl alcohol

As one of the most promising materials for the construction of desirable solid-state fluorescent system, new solid-state fluorescent host-guest system, which consists of the imidazo4,5-a]naphthalene-type fluorescent hosts 2 and sterically hindered guest molecules were designed and prepared. The crystals of 2 exhibit sensitive colour change and drastic fluorescence enhancement behaviour upon polyethers (diethylene glycol dimethyl ether (DGDM), diethylene glycol diethyl ether (DGDE) and diethylene glycol dibutyl ether (DGDB)) or tert-butyl alcohol. A comparison of the X-ray crystal structures of the guest-free and polyether- and tert-butyl alcohol-inclusion compounds indicates that the enclathrated polyether or tert-butyl alcohol molecule decrease the π-stacking between hosts and enlarge the distance between the host-host aromatic planes. On the bases of the spectral data and the crystal structures, the effects of the enclathrated sterically hindered guest on the drastic solid-state fluorescence enhancement behaviour of the host-guest crystals are discussed.